Baoding-FenShuaJiang
/
Green_GoodERP18_FSJ_Standard


			
				
					
						
						
							
							<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>19.13. Version and Platform Compatibility</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="runtime-config-locks.html" title="19.12. Lock Management" /><link rel="next" href="runtime-config-error-handling.html" title="19.14. Error Handling" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">19.13. Version and Platform Compatibility</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="runtime-config-locks.html" title="19.12. Lock Management">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="runtime-config.html" title="Chapter 19. Server Configuration">Up</a></td><th width="60%" align="center">Chapter 19. Server Configuration</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="runtime-config-error-handling.html" title="19.14. Error Handling">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="RUNTIME-CONFIG-COMPATIBLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">19.13. Version and Platform Compatibility</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="runtime-config-compatible.html#RUNTIME-CONFIG-COMPATIBLE-VERSION">19.13.1. Previous PostgreSQL Versions</a></span></dt><dt><span class="sect2"><a href="runtime-config-compatible.html#RUNTIME-CONFIG-COMPATIBLE-CLIENTS">19.13.2. Platform and Client Compatibility</a></span></dt></dl></div><div class="sect2" id="RUNTIME-CONFIG-COMPATIBLE-VERSION"><div class="titlepage"><div><div><h3 class="title">19.13.1. Previous PostgreSQL Versions</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="GUC-ARRAY-NULLS"><span class="term"><code class="varname">array_nulls</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.1.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        This controls whether the array input parser recognizes
        unquoted <code class="literal">NULL</code> as specifying a null array element.
        By default, this is <code class="literal">on</code>, allowing array values containing
        null values to be entered.  However, <span class="productname">PostgreSQL</span> versions
        before 8.2 did not support null values in arrays, and therefore would
        treat <code class="literal">NULL</code> as specifying a normal array element with
        the string value <span class="quote">“<span class="quote">NULL</span>”</span>.  For backward compatibility with
        applications that require the old behavior, this variable can be
        turned <code class="literal">off</code>.
       </p><p>
        Note that it is possible to create array values containing null values
        even when this variable is <code class="literal">off</code>.
       </p></dd><dt id="GUC-BACKSLASH-QUOTE"><span class="term"><code class="varname">backslash_quote</code> (<code class="type">enum</code>)
      <a id="id-1.6.6.16.2.2.2.1.3" class="indexterm"></a>
      <a id="id-1.6.6.16.2.2.2.1.4" class="indexterm"></a>
      </span></dt><dd><p>
        This controls whether a quote mark can be represented by
        <code class="literal">\'</code> in a string literal.  The preferred, SQL-standard way
        to represent a quote mark is by doubling it (<code class="literal">''</code>) but
        <span class="productname">PostgreSQL</span> has historically also accepted
        <code class="literal">\'</code>. However, use of <code class="literal">\'</code> creates security risks
        because in some client character set encodings, there are multibyte
        characters in which the last byte is numerically equivalent to ASCII
        <code class="literal">\</code>.  If client-side code does escaping incorrectly then a
        SQL-injection attack is possible.  This risk can be prevented by
        making the server reject queries in which a quote mark appears to be
        escaped by a backslash.
        The allowed values of <code class="varname">backslash_quote</code> are
        <code class="literal">on</code> (allow <code class="literal">\'</code> always),
        <code class="literal">off</code> (reject always), and
        <code class="literal">safe_encoding</code> (allow only if client encoding does not
        allow ASCII <code class="literal">\</code> within a multibyte character).
        <code class="literal">safe_encoding</code> is the default setting.
       </p><p>
        Note that in a standard-conforming string literal, <code class="literal">\</code> just
        means <code class="literal">\</code> anyway.  This parameter only affects the handling of
        non-standard-conforming literals, including
        escape string syntax (<code class="literal">E'...'</code>).
       </p></dd><dt id="GUC-ESCAPE-STRING-WARNING"><span class="term"><code class="varname">escape_string_warning</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.3.1.3" class="indexterm"></a>
      <a id="id-1.6.6.16.2.2.3.1.4" class="indexterm"></a>
      </span></dt><dd><p>
        When on, a warning is issued if a backslash (<code class="literal">\</code>)
        appears in an ordinary string literal (<code class="literal">'...'</code>
        syntax) and <code class="varname">standard_conforming_strings</code> is off.
        The default is <code class="literal">on</code>.
       </p><p>
        Applications that wish to use backslash as escape should be
        modified to use escape string syntax (<code class="literal">E'...'</code>),
        because the default behavior of ordinary strings is now to treat
        backslash as an ordinary character, per SQL standard.  This variable
        can be enabled to help locate code that needs to be changed.
       </p></dd><dt id="GUC-LO-COMPAT-PRIVILEGES"><span class="term"><code class="varname">lo_compat_privileges</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.4.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        In <span class="productname">PostgreSQL</span> releases prior to 9.0, large objects
        did not have access privileges and were, therefore, always readable
        and writable by all users.  Setting this variable to <code class="literal">on</code>
        disables the new privilege checks, for compatibility with prior
        releases.  The default is <code class="literal">off</code>.
        Only superusers can change this setting.
       </p><p>
        Setting this variable does not disable all security checks related to
        large objects — only those for which the default behavior has
        changed in <span class="productname">PostgreSQL</span> 9.0.
       </p></dd><dt id="GUC-OPERATOR-PRECEDENCE-WARNING"><span class="term"><code class="varname">operator_precedence_warning</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.5.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        When on, the parser will emit a warning for any construct that might
        have changed meanings since <span class="productname">PostgreSQL</span> 9.4 as a result
        of changes in operator precedence.  This is useful for auditing
        applications to see if precedence changes have broken anything; but it
        is not meant to be kept turned on in production, since it will warn
        about some perfectly valid, standard-compliant SQL code.
        The default is <code class="literal">off</code>.
       </p><p>
        See <a class="xref" href="sql-syntax-lexical.html#SQL-PRECEDENCE" title="4.1.6. Operator Precedence">Section 4.1.6</a> for more information.
       </p></dd><dt id="GUC-QUOTE-ALL-IDENTIFIERS"><span class="term"><code class="varname">quote_all_identifiers</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.6.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        When the database generates SQL, force all identifiers to be quoted,
        even if they are not (currently) keywords.  This will affect the
        output of <code class="command">EXPLAIN</code> as well as the results of functions
        like <code class="function">pg_get_viewdef</code>.  See also the
        <code class="option">--quote-all-identifiers</code> option of
        <a class="xref" href="app-pgdump.html" title="pg_dump"><span class="refentrytitle">pg_dump</span></a> and <a class="xref" href="app-pg-dumpall.html" title="pg_dumpall"><span class="refentrytitle"><span class="application">pg_dumpall</span></span></a>.
       </p></dd><dt id="GUC-STANDARD-CONFORMING-STRINGS"><span class="term"><code class="varname">standard_conforming_strings</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.7.1.3" class="indexterm"></a>
      <a id="id-1.6.6.16.2.2.7.1.4" class="indexterm"></a>
      </span></dt><dd><p>
        This controls whether ordinary string literals
        (<code class="literal">'...'</code>) treat backslashes literally, as specified in
        the SQL standard.
        Beginning in <span class="productname">PostgreSQL</span> 9.1, the default is
        <code class="literal">on</code> (prior releases defaulted to <code class="literal">off</code>).
        Applications can check this
        parameter to determine how string literals will be processed.
        The presence of this parameter can also be taken as an indication
        that the escape string syntax (<code class="literal">E'...'</code>) is supported.
        Escape string syntax (<a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS-ESCAPE" title="4.1.2.2. String Constants with C-Style Escapes">Section 4.1.2.2</a>)
        should be used if an application desires
        backslashes to be treated as escape characters.
       </p></dd><dt id="GUC-SYNCHRONIZE-SEQSCANS"><span class="term"><code class="varname">synchronize_seqscans</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.2.2.8.1.3" class="indexterm"></a>
      </span></dt><dd><p>
        This allows sequential scans of large tables to synchronize with each
        other, so that concurrent scans read the same block at about the
        same time and hence share the I/O workload.  When this is enabled,
        a scan might start in the middle of the table and then <span class="quote">“<span class="quote">wrap
        around</span>”</span> the end to cover all rows, so as to synchronize with the
        activity of scans already in progress.  This can result in
        unpredictable changes in the row ordering returned by queries that
        have no <code class="literal">ORDER BY</code> clause.  Setting this parameter to
        <code class="literal">off</code> ensures the pre-8.3 behavior in which a sequential
        scan always starts from the beginning of the table.  The default
        is <code class="literal">on</code>.
       </p></dd></dl></div></div><div class="sect2" id="RUNTIME-CONFIG-COMPATIBLE-CLIENTS"><div class="titlepage"><div><div><h3 class="title">19.13.2. Platform and Client Compatibility</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="GUC-TRANSFORM-NULL-EQUALS"><span class="term"><code class="varname">transform_null_equals</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.16.3.2.1.1.3" class="indexterm"></a>
      <a id="id-1.6.6.16.3.2.1.1.4" class="indexterm"></a>
      </span></dt><dd><p>
        When on, expressions of the form <code class="literal"><em class="replaceable"><code>expr</code></em> =
        NULL</code> (or <code class="literal">NULL =
        <em class="replaceable"><code>expr</code></em></code>) are treated as
        <code class="literal"><em class="replaceable"><code>expr</code></em> IS NULL</code>, that is, they
        return true if <em class="replaceable"><code>expr</code></em> evaluates to the null value,
        and false otherwise. The correct SQL-spec-compliant behavior of
        <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> is to always
        return null (unknown). Therefore this parameter defaults to
        <code class="literal">off</code>.
       </p><p>
        However, filtered forms in <span class="productname">Microsoft
        Access</span> generate queries that appear to use
        <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> to test for
        null values, so if you use that interface to access the database you
        might want to turn this option on.  Since expressions of the
        form <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> always
        return the null value (using the SQL standard interpretation), they are not
        very useful and do not appear often in normal applications so
        this option does little harm in practice.  But new users are
        frequently confused about the semantics of expressions
        involving null values, so this option is off by default.
       </p><p>
        Note that this option only affects the exact form <code class="literal">= NULL</code>,
        not other comparison operators or other expressions
        that are computationally equivalent to some expression
        involving the equals operator (such as <code class="literal">IN</code>).
        Thus, this option is not a general fix for bad programming.
       </p><p>
        Refer to <a class="xref" href="functions-comparison.html" title="9.2. Comparison Functions and Operators">Section 9.2</a> for related information.
       </p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="runtime-config-locks.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="runtime-config.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="runtime-config-error-handling.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">19.12. Lock Management </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 19.14. Error Handling</td></tr></table></div></body></html>